The present invention refers to an electric heating system, the heating power of which is adjustable by a control means.
Electric heatings or heating systems are, for example, required for different applications in motor vehicles, for example for heating the air within the vehicle, for pre-heating the cooling water in water-cooled engines, for pre-heating the spark plugs in self-igniting internal combustion engines, for heating the fuel (diesel) etc. Heating systems of that kind usually consist of a heating with at least one heating stage, each comprising at least one heating element (for example provided as a heating resistor) for generating a predetermined heating power, as wellas of a control unit for monitoring the chronological course and for defining the heating power; the heating and the control unit are provided as separate modules (functional units) and are arranged at different positions within the motor vehicle.
It is a disadvantage that on one hand a plurality of connection lines is required between the heating and the control unit (which is connection with space requirements, costs, electromagnetical compatibility problems) and that on the other hand the dissipation power has to be carried off separately.
The control unit can be realized so as to control the different controllers which cause different control responses upon occurrence of a control deviation or control difference; proportional controller, integral controller, differential controller, linear controller or switchable step controllers are for example conmmonly used. In order to reduce the load of the control means, said control means may be composed of a plurality of controllers that are generally formed as switchable step controllers and may be activated or deactived for example by switching operations. The problem that occurs in this case (in particular in step controllers) is the delimitation of the range of action of the different controllers, i.e. the transition between the control ranges of the controllers is not clearly defined; this will lead to interferences of the control or of the control response (occurrence of dead ranges, overlappings, hystereses, undefined conditions etc.) and electromagnetical compatibility interferences, the reduction of which requiring expensive components